Question: Christopher is 3 times as old as Ishaan and is also 12 years older than Ishaan. How old is Christopher?
Answer: We can use the given information to write down two equations that describe the ages of Christopher and Ishaan. Let Christopher's current age be $c$ and Ishaan's current age be $i$ $c = 3i$ $c = i + 12$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $c$ is to solve the second equation for $i$ and substitute that value into the first equation. Solving our second equation for $i$ , we get: $i = c - 12$ . Substituting this into our first equation, we get the equation: $c = 3$ $(c - 12)$ which combines the information about $c$ from both of our original equations. Simplifying the right side of this equation, we get: $c = 3c - 36$ Solving for $c$ , we get: $2 c = 36$ $c = 18$.